As is known in the art, a model is a representation or approximation of a real world process, device or concept. A model can be implemented in computer code for execution on a processor in order to allow a user to rapidly vary model parameters and to understand the impact on the process, device or concept of varying such parameters.
A project planning model is a model that can be used to plan a project (e.g. a construction project). Some well-known project planning models include a dependency structure matrix (DSM), a critical path method (CPM), a precedence diagram method (PDM), a concurrent engineering technique, a critical chain technique, an overlapping framework technique, various system dynamics techniques, a simulation language for alternative modeling technique (SLAM), a graphical evaluation and review technique (GERT), a queue graphical evaluation and review technique (Q-GERT), and a program evaluation and review technique (PERT). Such conventional project planning models are used to plan and control projects.
As mentioned above, such models can be implemented in as computer code for execution on a processor to provide computer implemented project management tools which can be used to aid in the planning and management of projects such as construction projects and the like. In this manner, computer tools which apply the principles of particular project planning models are provided. Such tools provide a project manager with the ability to generate an initial project plan and to update and modify the project plan thereafter.
As is also known, a so-called “network based” project planning model provides a model of a project plan having activities and time relationship linkages between the activities. A database underlying the conventional project planning model will be referred to herein as conventional project plan data, having conventional project plan data elements. Of the above-mentioned techniques, CPM, PDM, PERT, and GERT will be recognized to be the most common network based project planning models.
Conventional project plan data elements of PDM, for example, include a list of activities, an activity duration value for each activity, and time precedence relationships between the activities. A time precedence relationship describes a relationship between two activities. For example if a first activity must finish before a second activity can start, the first and second activities are said to be in a “finish to start” time precedence relationship. Time precedence relationships include finish to start (FS), finish to finish (FF), start to finish (SF), and start to start (SS) relationships. The time precedence relationships can also include lead or lag times. For example, when two activities are related in an FS time precedence relationship, a downstream activity is planned to start at the completion of an upstream activity to which it is related. For another example, when two activities are time related in an FS relationship with lead, a downstream activity can begin a lead period before the completion of an upstream activity to which it is related. This is contrasted with an FS relationship with lag for which the downstream activity is delayed to start with a lag delay after the completion of an upstream activity to which it is related.
Contingency time buffers, also called contingency buffers, are conventionally applied to the end of one or more activities in the project plan to absorb the effect of time delay, or slippage, of individual activities. Contingency buffers attempt to ensure that the total time duration of the project is preserved even when the durations of individual activities expand, either from expected or from unexpected changes.
To the conventional project plan data elements above, PERT and GERT add various other conventional project plan data elements. PERT, for example, includes probability values associated with the duration value of each activity. The probability value assigns a probability to the likelihood that an activity will be completed within its scheduled duration. PERT also adds a path probability value to each time precedence relationship. The path probability value corresponds to the likelihood that a time precedence relationship will be achieved as planned. GERT adds probabilistic time precedence relationship branching.
Conventional project planning models that utilize contingency buffers are generally inefficient in protecting the project schedule performance. Once added to the duration of an activity, a contingency buffer can be considered by those workers performing the activity to be part of the original time schedule of the activity without distinction. When workers realize that they have extra time to complete a task, their work tends to expand to fill the perceived extra time, creating an indeterminate duration. As a result, the contingency buffer generally does not function effectively to protect the initially planned overall schedule duration.
Furthermore, when contingency buffers are applied to a project plan at a “merging point,” no benefit is gained to the overall project schedule from an activity that finishes early at the merging point. A merging point will be understood to be a place in a project plan at which a first and a second activity both have a time precedence relationship with a third activity.
Therefore, it would be desirable to provide a project planning method as part of a project planning model that has the ability to absorb time slippages and project changes yet which does not tend to expand a project schedule when such slippages and changes occur. It would be further desirable to provide a project planning method with which the overall project schedule benefits from the early completion of activities at a merging point.